2,428 research outputs found
Riemannian Geometry of Noncommutative Surfaces
A Riemannian geometry of noncommutative n-dimensional surfaces is developed
as a first step towards the construction of a consistent noncommutative
gravitational theory. Historically, as well, Riemannian geometry was recognized
to be the underlying structure of Einstein's theory of general relativity and
led to further developments of the latter. The notions of metric and
connections on such noncommutative surfaces are introduced and it is shown that
the connections are metric-compatible, giving rise to the corresponding Riemann
curvature. The latter also satisfies the noncommutative analogue of the first
and second Bianchi identities. As examples, noncommutative analogues of the
sphere, torus and hyperboloid are studied in detail. The problem of covariance
under appropriately defined general coordinate transformations is also
discussed and commented on as compared with other treatments.Comment: 28 pages, some clarifications, examples and references added, version
to appear in J. Math. Phy
Interplay between bending and stretching in carbon nanoribbons
We investigate the bending properties of carbon nanoribbons by combining
continuum elasticity theory and tight-binding atomistic simulations. First, we
develop a complete analysis of a given bended configuration through continuum
mechanics. Then, we provide by tight-binding calculations the value of the
bending rigidity in good agreement with recent literature. We discuss the
emergence of a stretching field induced by the full atomic-scale relaxation of
the nanoribbon architecture. We further prove that such an in-plane strain
field can be decomposed into a first contribution due to the actual bending of
the sheet and a second one due to edge effects.Comment: 5 pages, 6 figure
Programmed buckling by controlled lateral swelling in a thin elastic sheet
Recent experiments have imposed controlled swelling patterns on thin polymer
films, which subsequently buckle into three-dimensional shapes. We develop a
solution to the design problem suggested by such systems, namely, if and how
one can generate particular three-dimensional shapes from thin elastic sheets
by mere imposition of a two-dimensional pattern of locally isotropic growth.
Not every shape is possible. Several types of obstruction can arise, some of
which depend on the sheet thickness. We provide some examples using the
axisymmetric form of the problem, which is analytically tractable.Comment: 11 pages, 9 figure
Hazard assessment of storm events in the central region of the Portuguese coast
The environmental and socio-economic importance of the coastal areas is widely recognized, but these areas face today severe weaknesses and high-risk situations. The increased demand and human occupation of the coast has greatly contributed to increase such weaknesses. Today, throughout the world, in all countries with coastlines, episodes of waves overtopping and coastal flooding are frequent. These episodes are usually responsible for property losses and often put human lives at risk. The floods are caused by coastal storms due to the action of very strong winds. The propagation of these storms towards the coast induces high water levels.
Consequently, carrying out series of storm scenarios and analyzing their impacts through numerical modelling is of prime interest to the coastal decision-makers. A contribution to the preservation and sustainability of the coastal zone constitutes the main aim of this work. Firstly, historical storm tracks and intensities are characterized for the Portuguese coast, in terms of probability of occurrence. Secondly, several storm events with high potential of occurrence are generated using the specific tool DelftDashboard. The hydrodynamic model Delft3D is then used to simulate their effects on currents and on the coastal water levels. Two spatial domains are considered: a large domain encompassing the Iberian coastal zone and a smaller domain for the central region of the Portuguese coast (between cities of Aveiro and Figueira da Foz); this one with a more refined grid. Based on statistical data and by numerical modelling, a review of the impact of coastal storms to different locations within the study area is performed
Variação de procedências para a produção de sementes de Araucaria angustifolia Bert. O. Ktze.
Resumo
Seletividade do óleo de mamona em adultos do Trichogramma pretiosum Riley, 1978 (Hymenoptera: Trichogrammatidae).
Testes de seletividade tornaram-se obrigatórios quando o objetivo é estudar o efeito de um inseticida, mesmo que de origem vegetal, em organismos benéficos. Neste sentido, foi avaliada a seletividade do Óleo de mamona® nas concentrações de 1, 2, 3, 4, 5 e 6% (v/v), do detergente neutro Zupp® a 2% (v/v) (emulsificante para o óleo), do inseticida clorpirifós a 0,5 L i.a./ha (testemunha positiva) e da água destilada em adultos do T. pretiosum, de acordo com protocolos da IOBC/WPRS.Resumo
Soliton surfaces associated with symmetries of ODEs written in Lax representation
The main aim of this paper is to discuss recent results on the adaptation of
the Fokas-Gel'fand procedure for constructing soliton surfaces in Lie algebras,
which was originally derived for PDEs [Grundland, Post 2011], to the case of
integrable ODEs admitting Lax representations. We give explicit forms of the
\g-valued immersion functions based on conformal symmetries involving the
spectral parameter, a gauge transformation of the wave function and generalized
symmetries of the linear spectral problem. The procedure is applied to a
symmetry reduction of the static -field equations leading to the
Jacobian elliptic equation. As examples, we obtain diverse types of surfaces
for different choices of Jacobian elliptic functions for a range of values of
parameters.Comment: 14 Pages, 2 figures Conference Proceedings for QST7 Pragu
Viabilidade econômica do sistema agroflorestal grevílea x café na Região Norte do Paraná.
Na década de 70, o Instituto Brasileiro do Café - IBC incentivou a introdução de Grevillea robusta nos cafezais da região Norte do Paraná, na forma de quebra-ventos, apesar de sua implantação não haver seguido padrões técnicos adequados. Para a análise da viabilidade econômica da utilização desses quebra-ventos, foram comparados os benefícios diretos (custos x renda) do Sistema Puro Café e do Sistema Agroflorestal Grevílea x Café, utilizando um aplicativo de apropriação e análise de custos, o SAAC florestal (Hildebrandt, 1995). As planilhas do aplicativo foram preenchidas separadamente para os dois sistemas. O Sistema Puro Café contou com dados secundários de custos de produção e rendas fornecidos por órgãos públicos e privados. Para a análise do Sistema Agroflorestal, foram utilizados os mesmos dados referentes à produção monocultural de café, acrescidos dos dados de custos de produção e rendas da espécie florestal obtidos por meio de questionários aplicados junto a proprietários rurais e serrarias da região de estudo. Os resultados obtidos permitiram constatar que a espécie florestal introduzida no sistema representa um custo adicional insignificante para o produtor rural e ocupa uma área mínima, ou seja, uma média de 58 árvores por hectare. A renda obtida com a venda da madeira para serrarias gera um aumento significativo da renda no último ano, de 32,22%, permitindo o pagamento dos custos de implantação ou grande parte dos custos de reforma da atividade. Portanto, a utilização da grevílea nos cafezais é altamente positiva do ponto de vista do aumento da rentabilidade da atividade e da tranquilidade do produtor, pois pode representar uma poupança ao longo do ciclo da cultura cafeeira, assegurando a continuidade desta atividade por meio do pagamento da reforma com o corte da madeira
Contribution to the preservation of healthy coastal ecosystems
The release of pollutants into coastal zones from municipal and/or industrial
drainage systems is a problem with a considerable environmental impact. In
order to minimize the contamination of coastal waters in certain places (e.g.,
along beaches and in aquacultures), solutions based on the construction of
submarine sewer outfalls have been proposed. In order to ascertain the optimal
conditions for the release of an emissary, in particular the place of release, it is
necessary to characterize the hydrodynamic transport processes that govern the
evolution and mixture of pollutants in the area of interest. Circulation in the
coastal zone is complicated, given that it is determined by a set of forcing
mechanisms of diverse origins (meteorological, astronomical, large-scale ocean
circulation, etc.) that endow it with a considerable space-time variation.
Wastewater plume behaviour and characteristics depend both on the receiving
water conditions and on the discharge characteristics. Accordingly, the
implementation of a submarine outfall system requires a prior study of the site
where the outfall is to be constructed, in order to achieve optimal rates of dilution
of the pollutants released to the environment. Mathematical modelling appears to
be a very useful tool for coastal zone environmental management either for
continuous monitoring analysis or in accidental ecosystem rupture. This work
presents some results and conclusions of two case studies. The first is a
study of the pollutant cloud released at the São Jacinto submarine sewer
outfall, located about 3 km offshore and 3 km north of an important
coastal lagoon (NW Portugal). The main focus of this study was to
establish the hydrodynamic conditions in which the pollutant release
might affect the coastline (principally the existing beaches and lagoon).
The second case presents some hydrodynamic results and water quality
aspects of the Ria de Arosa (NW Spain), and also includes an assessment
of the environmental impact of wastewater discharges from nine
submarine outfalls considered in the sanitation plan of this bay. Results of
faecal matter concentration distribution were used in the discussion on the
outfall discharges’ impact on the natural water system for different
hydrodynamic scenarios. In both cases, 3D numerical models were used
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